You could call them early bloomers: In 2010 and 2012, plants in the eastern U.S. produced flowers earlier than at any point in recorded history, a new study says.

This result, according to the research team, has a bit of a literary twist: It comes from data collected by U.S. environmental writers Henry David Thoreau and Aldo Leopold. Thoreau began observing bloom times in Massachusetts in 1852, and Leopold began in Wisconsin in 1935.

Scientists compared this historical data with modern, record-shattering high temperatures in Massachusetts and Wisconsin during 2010 and 2012. (See “Heat Waves ‘Almost Certainly’ Due to Global Warming?”)

They discovered that those two recent warm spells triggered many spring-flowering plants to blossom up to 4.1 days earlier for every 1.8-degrees Fahrenheit (degree Celsius) rise in average spring temperatures.